1. Field of the Invention
Example embodiments generally relate to a heating device, a fixing device, and an image forming apparatus, and more particularly, to a heating device for heating a fixing member that applies heat to a toner image on a recording medium, a fixing device including the heating device, and an image forming apparatus including the fixing device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then collects residual toner not transferred and remaining on the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such fixing device may include a fixing roller that generates heat by electromagnetic induction heating and a pressing roller pressed against the fixing roller to form a fixing nip between the fixing roller and the pressing roller. As a recording medium bearing a toner image passes through the fixing nip between the fixing roller and the pressing roller, the fixing roller and the pressing roller apply heat and pressure to the recording medium to melt and fix the toner image on the recording medium. Thereafter, the recording medium bearing the fixed toner image is discharged from the fixing nip.
The heat applied by the fixing roller to the recording medium may be caused by a coil facing the fixing roller by induction heating. Specifically, when an electric current is applied to the coil facing the fixing roller, the coil generates a magnetic field that causes the fixing roller to generate an eddy current. The eddy current causes the fixing roller to generate heat. Such heat generation of the fixing roller may be controlled by a temperature sensor that detects the temperature of the fixing roller so as to maintain the proper temperature of the fixing roller for fixing. For example, a contact sensor (e.g., a thermistor) can be disposed in contact with the outer circumferential surface of the fixing roller to detect the temperature of the outer circumferential surface of the fixing roller. Alternatively, a non-contact sensor (e.g., a thermopile), which is separated from the fixing roller and receives infrared rays radiated from the outer circumferential surface of the fixing roller, detects the temperature of the outer circumferential surface of the fixing roller based on the received infrared rays.
However, the non-contact sensor has a drawback in that steam generated in a gap between the coil and the fixing roller or wax volatilized from toner on the fixing roller, which is transferred from the toner image on the recording medium, may adhere to the non-contact sensor, thereby degrading the sensor's sensitivity. For example, the non-contact sensor faces the fixing roller via a through-hole provided in the coil to detect the temperature of the fixing roller via the through-hole of the coil. The steam generated in the gap between the coil and the fixing roller and the wax volatilized from toner on the fixing roller may move through the through-hole of the coil and adhere to the non-contact sensor facing the through-hole. Accordingly, the steam and the wax adhered to the non-contact sensor may cause erroneous detection of the non-contact sensor, resulting in formation of a faulty toner image or malfunction and burning of the fixing device due to unstable control of the temperature of the fixing roller.